1. Field of the Invention
The present invention relates generally to a bolt for fastening two structural members together and more particularly to a bolt having an integral locking member to prevent rotation of the bolt.
2. Description of the Prior Art
In the nuclear power industry there is serious concern of SCC (Stress Corrosion Cracking) and IASCC (Irradiation Assisted Stress Corrosion Cracking) failures of threaded bolts/fasteners having external threads in aqueous environments.
There is also a concern of the threaded fastener losing its pre-load and counter-rotating (backing out). Historically the solution to prevent counter-rotation and loss of pre-load was the use of a locking cup (either integral to the fastener head or two-piece) which is mechanically deformed (crimped) into a detent in the counter-bore wall of the part to be fastened. Such mechanical deformation produces permanent strain and residual stresses which increase the risk of SCC. The resultant use of this methodology is a SCC susceptible fastener that requires a two step installation process (torque, crimp) for installation in nuclear containment. The process is time consuming and hence expensive and also presents risk due to the possibility of parts falling into the reactor.
Further details and examples of such prior art bolts presently used in the nuclear power industry may be found in at least the following U.S. Patents wherein U.S. Pat. No. 4,711,760 issued to Blaushild teaches the use of a bolt to secure two reactor plates and which has a retainer cap screwed over the inserted bolt to prevent counter-rotation and U.S. Pat. No. 6,164,886 issued to Matarazzo et al. which also teaches a retainer bolt for securing two reactor plates while preventing anti-rotation thereof. In the Matarazzo patent his is done by forming a series of circumferential detents in the plate member and providing the bolt head with a deformable circumferential crown which is deformed to fit into the member's detents. This locks the bolt to the member and prevents counter-rotation.
Clearly such bolts while preventing counter-rotation are not capable of being removed to check or replace the parts they are holding together and then being reused.